1. Field of the Invention
The present invention relates generally to an illuminating system using a fly's eye lens and, more particularly, to an illuminating system suitable for a liquid crystal video projector. The present invention also relates to a projection apparatus employing this illuminating system and to a detecting apparatus using the illuminating system.
2. Related Background Art
In general, a liquid crystal video projector is exemplified as an apparatus for projecting a video image on a large screen. The liquid crystal video projector is roughly classified into a phase modulation type in which a polarizing optical system is combined with a double refraction property of the liquid crystal's own and a scatter type in which a Schlieren optical system is combined with the liquid crystal assuming a light scattering property as in the case of a polymer dispersion type liquid crystal.
Herein, FIG. 1 illustrates one example of the latter type, i.e., a conventional dispersion type liquid crystal video projector in which the Schlieren optical system is combined with the liquid crystal exhibiting the light scattering property. Referring to FIG. 1, beams of illumination light emitted from a light source 91 are substantially collimated by a condenser lens 92 and, thereafter, fall on a reflecting surface of a light valve 96.
The light beams reflected by the light valve 96 are guided to a projection optical system. At this time, however, a space modulation concurrently takes place on the light valve 96. For example, a portion for partially scatter-reflecting the light beams falling on the light valve 96 is formed by a method such as deforming a surface of an oil film or metal film by use of an electronic element. When the irradiation light beams are reflected therefrom, the space modulation is effected by generating direct reflection light and scatter reflection light. Then, an image is formed by selecting the direct reflection light or the scatter reflection light from the light valve 96, thereby projecting on-the-light-valve video data.
In the example of the prior art shown in FIG. 1, the light beams direct-reflected from the light valve 96 are condensed by a condenser lens 910 and, thereafter, eliminated as unnecessary light beams by a light absorbing member 911. The light beams partially scatter-reflected from the light valve 96 are converged by a projection lens 87 and projected on a screen 98.
As described above, the illumination light beams with which the light valve 96 is irradiated from the illumination optical system constructed of the light source 91 and the condenser lens 92, etc. are space-modulated on the light valve 96 and thereafter guided to the projection optical system composed of the projection lens 97, etc. The light beams are then projected on the screen 98.
In the conventional projection apparatus described above, an illuminance of the irradiation light beams in each intra-section area thereof is not uniform depending on the light source of the illumination optical system. Consequently, it may happen that an ununiformity in terms of luminance on the screen is produced in a projected image projected based thereon. For this reason, it can be considered that a fly's eye lens is used as a method of uniformizing the illuminance of the illumination light beams.
This fly's eye lens is a combination of a multiplicity of lens elements as illustrated in FIG. 2. The illuminance of the illumination light beams can be uniformized by incorporating this fly's eye lens into the illumination optical system.
FIG. 2 illustrates one example of a layout of the typical illumination optical system using the fly's eye lens. Referring to FIG. 2, a light source 81 consisting of a lamp 81a and an elliptical mirror 81b and an irradiated surface 89 are disposed in a face-to-face relationship with each other. The light beams emitted from the light source 81 are substantially collimated by a condenser lens 82 and thereafter incident on a fly's eye lens 83.
The light beams incident on the fly's eye lens 83 are split and converged by its respective lens elements and thereafter incident on a relay lens 85 while being dispersed. The same area on the irradiated surface 89 is irradiated with the respective light beams through the relay lens 85. Accordingly, this irradiated surface 89 is irradiated with the light beams with an uniform intensity.
If the projection apparatus can be combined with the fly's eye lens as shown in FIG. 2, a problem in terms of the ununiform luminance of the projected image can be obviated. This fly's eye lens does not generally, however, exhibit an uniformizing effect unless the optical axis of the light beams incident on the fly's eye lens is orthogonal to the irradiated surface and the incident surface of the fly's eye lens.
Hence, the uniformizing effect of the intensity of the illumination light beams can not be expected simply by incorporating the fly's eye lens into the illumination optical system of the scatter type projection apparatus constructed so that the optical axes of the two optical systems are spatially tilted to the light valve.
Another method of solving the problem of the ununiformity of the intensity of this projected image, it can be also considered, entails uniformizing the intensity of the illumination light beams by performing an optical path synthesizing/splitting process with the aid of a half-mirror instead of the fly's eye lens. According to such a method, however, there is caused a loss of light quantity due to half-transmitting (reflecting) light via the half-mirror, and hence there arises a problem in which the light quantity of a video data image that is finally projected decreases on the whole.
Further, the irradiation light beams are space-modulated into the scattered reflection light and the direct reflection light on the light valve, and, therefore, the direct reflection light exhibiting a higher illuminance is eliminated as unnecessary light beams (the scattered reflection light is selected and projected). Consequently, there also exists such a problem that the quantity of the light projected on the screen is reduced on the whole, resulting a darker projected image.
As discussed above, in the conventional scatter type projection apparatus employing the Schlieren optical system, if the partial ununiformity of the illuminance appears in the illumination light beams from the light source, the unevenness in terms of the luminance is easy to occur in the projected image. When effecting the optical path synthesizing/splitting process to obviate this luminance ununiformity, the problem is that the light quantity of the finally projected video data image decreases on the whole.
Under such circumstances, there is proposed a method (Japanese Utility Model Publication No. 60-41538) of making use of the direct reflection light to increase the light quantity of the finally projected video data image. Based on this method of making use of the direct reflection light, however, the uniformizing effect of the intensity of the illumination light beams can not be expected.
Further, it is required that such a scatter type projection apparatus be constructed to cause no interference between the illumination optical system and the projection optical system. Accordingly, it is a general configuration that the optical axes of the two optical systems are, as in the conventional example shown in FIG. 1, spatially tilted to the light valve. Using such an oblique incident (reflecting) light beam entails a problem in which the image projected on the screen is resultantly distorted.
This image distortion can be obviated by shifting the projection optical system. According to this method, however, a projection optical system's demand performance needed for shifting the projection optical system becomes more strict, which in turn induces another problem of leading to an increase in costs.
Also, in the case of employing the fly's eye lens as depicted in FIG. 2, the projected image is to be distorted based on the configuration wherein the optical axes of the two optical systems are spatially tilted to the light valve.
Moreover, in the example also which is disclosed in Japanese Utility Model Publication No. 60-41538 given above, the distortion of the projected image still remains unobviated.